The measurement of gas flow is becoming increasingly more important in the application and control of many processes, as well as in the research laboratory. To assure accuracy in the measurement of gas flow, the flow meter is calibrated against a higher level flow standard. One of the accepted primary standards for gas flow measurement and calibration is the use of a vertically oriented precision bore flowtube and mercury-wetted piston. Although this device is quite precise, it is also very expensive and very large. Another standard for gas flow measurement is the bubble flow meter. In the basic form of the bubble flow meter, a soap film is generated from a soap solution which is propelled by the gas flow under measurement from one end of the flow meter to the other. By timing the rise of the soap film between calibrated volume marks, the volume flow is obtained. Although it is generally agreed that the bubble flow meter accuracy may be affected by changes in ambient conditions such as, humidity and temperature and is dependent upon the gas flow rate, it is understood that these factors can be readily corrected or compensated for in a laboratory setting. This is not, however, as easily done in a field setting or in a commercial process environment. Moreover, the bubble flow meter is a cumbersome and generally unwieldy instrument to use as compared to a reciprocating piston flow meter, particularly under field conditions. A flow meter, which uses a positive displacement piston comparable in operation to the mercury-wetted piston, but substantially smaller in size, weight, and cost, would have substantial utility for field use.